The field is a process and apparatus for selectively hydrogenating diolefins in a cracked stream.
Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. Various products may be produced from such a process, including a naphtha product and/or a light product such as propylene and/or ethylene.
Delayed coking is a thermal cracking process used in petroleum refineries to upgrade and convert petroleum residuum, which are typically the bottoms from atmospheric and vacuum distillation of crude oil, into gas and liquid product streams leaving behind petroleum coke as a solid concentrated carbon material. In the practice of delayed coking process, a hydrocarbon residuum is heated to coking temperature in a coker furnace, and the heated residuum is then passed to a coking drum where it decomposes into volatile components and delayed coke. The delayed coking process has been used for several decades, primarily as a means of producing useful products from the low value residuum of a petroleum refining operation.
Gasoline regulations are increasingly creating a need to treat various refinery streams and products. The petroleum distillates often contain unwanted heteroatom contaminants such as sulfur and nitrogen. In addition to sulfur and nitrogen compounds, mixed refinery streams contain a broad spectrum of olefinic compounds. This is especially true of products from delayed coking, fluidized catalytic cracking, ebullated-bed cracking, and/or slurry cracking which crack heavier hydrocarbon molecules into lighter hydrocarbon molecules by a hydrogen transfer mechanism. Diolefins in cracked naphtha streams can be detrimental in further downstream processing due to fouling via polymerization of tri- and di-unsaturated hydrocarbons and nitrogen species and act as catalyst poisons in petrochemicals applications like in the manufacture of polypropylene and tertiary amyl methyl ether.
Therefore, there is a need for a new process configuration to convert the cracked streams from conversion units like FCC and delayed coking units containing at least tri- and di-unsaturated hydrocarbon, mercaptans, sulfides and/or nitrogen compounds to prevent undesirable conditions in downstream applications. Conventionally, removal of di- and tri-olefins from recovered product streams, i.e., the liquefied petroleum gas (LPG) and naphtha streams, is typically accomplished separately, downstream of the gas recovery section. There is a need for improved processes to remove the di- and tri-olefins from the naphtha and LPG streams in an efficient manner.